I'm afraid you can't. Even if you buy Speechdio Business without the Standard Version, you will not be able to login.
Here is why:
1. Speechdio Standard is the main product which is either an Yearly Subscription or Monthly Subscription.
2. Speechdio Business is an Upgrade or Up-sell which adds the Business features in your Speechdio account.
3. Since Speechdio Business is not independent, you will need to subscribe for the main product Speechdio yearly or monthly subscription first. Else you can't login with only Speechdio Business in your account.